Multi-ply fibrous sheets having a wet-laid ply and a dry-laid ply

Abstract

A process and apparatus for forming a multi-ply sheet of cellulosic fibrous material. A dry-laid mat and a wet-laid web of cellulosic fibers are joined together and concurrently the dry-laid mat is consolidated by the concurrent application of heat, pressure and moisture, the moisture being derived from the wet-laid web.

We claim: 
     
       1. A process for forming a multi-ply sheet of cellulosic fibrous material comprising the steps of: dry-laying a mat of cellulosic fibrous material by depositing cellulosic fibers in a dry state via an airstream onto a main forming band to a thickness sufficient to form a distinct ply within a multi-ply sheet after the fibers of the mat have been caused to adhere together by the concurrent application of heat, moisture and pressure,   forming a web of cellulosic fibrous material by a wet-forming technique on an auxiliary forming band,   joining the web and the mat together under sufficient pressure to join them into a multi-ply sheet while concurrently consolidating the fibers of the dry-laid mat into a strong discernable ply by concurrently subjecting the mat to all three of moisture, heat greater than 150° F. and pressure of not less than 50 p.s.i. by passing the joined multi-ply sheet through at least one press nip formed between at least one press roll and a heated cylinder wherein the dry-laid mat receives at least a major portion of the moisture it requires for such strength by transfer of moisture from the wet-laid web to the dry-laid mat.   
     
     
       2. A process according to claim 1, wherein the wet-formed web is formed with a moisture content sufficient to provide substantially all of the moisture required by the dry-laid fibrous mat during the consolidating step. 
     
     
       3. A process according to claim 1, wherein said pressure is repeatedly applied in a plurality of press nips formed between a plurality of press rolls and said heated cylinder. 
     
     
       4. A process according to claim 1, wherein the wet-formed web is formed using a cylindrical mold machine. 
     
     
       5. A process according to claim 1 wherein the heat is applied at a temperature of greater than 200° F. 
     
     
       6. An apparatus for forming a multi-ply sheet of cellulosic fibrous material comprising: means for dry-laying a mat of cellulosic fibrous material including means for depositing cellulosic fibers in a dry state via an airstream onto a main forming band up to a thickness sufficient to form a distinct ply within a multi-ply sheet after the fibers of the mat have been caused to adhere together by the concurrent application of heat, moisture and pressure,   an auxiliary forming band and means for forming a web of cellulosic fibrous material on said auxiliary forming band by a wet-forming process,   means for joining the mat and the web together under sufficient pressure to join them into a multi-ply sheet,   and means including at least one press roll and a heated cylinder forming at least one nip therebetween for consolidating the fibers of the dry-laid mat into a strong discernable ply by concurrently subjecting the mat to all three of moisture, heat greater than 150° F. and pressure of not less than 50 p.s.i. while the joined mat and web pass through said nip, and wherein the moisture for such consolidation is provided from said wet-laid web.   
     
     
       7. Apparatus according to claim 6, wherein said wet-web forming means comprises a cylinder mold machine.